Performance Of Treating DO Mestic Sewage With Hybrid Process Of Coagulation- Trick Ling Filter- Ultrafiltration And Properties Of DOM

As the current biological wastewater treatment technologies exist many dis-advantages, such as the higher energy consumption, the larger production of sludge and so on, the development of new technology for wastewater treatment with less investment, lower operation cost and energy saving is imperative. This paper pre-sented the coagulation-ultrafiltration process for the domestic sewage treatment and investigated the performance of the hybrid process. Based on the analysis of the effluent quality, a new process combining the trickling filter with the coagula-tion-ultrafiltration process called coagulation-trickling filter-ultrafiltration was used to treat the domestic sewage. This paper discussed the factors influencing the re-moval effect of COD, ammonia and total phosphorus (TP). The properties of dis-solved organic matter (DOM) were also investigated.In the coagulation-ultrafiltration system, the coagulation improved the mem-brane flux by shifting the particle size distribution to larger zone, removing the or-ganic matter between 3 kDa and 100 kDa and reducing the pollutant load. The dose of coagulant was an important factor affecting the membrane flux. The analysis of the membrane fouling resistance and the Field model indicated that the main resis-tance was from the cake/gel layer formation when the sewage after coagulation passed through the ultrafiltration membrane. The recovery effect of membrane flux by back-flushing decreased as increased frequency, and the chemical cleaning with NaClO recovered 90% of the initial membrane flux. About 95% of SS, 60%~70% of COD and 85% of TP were removed by this process, but the removal of ammonia was not good.A new process combined trickling filter (TF) with the coagulation- ultrafiltra-tion was designed to remove more COD and ammonia. The carbon oxidation and nitrification of the trickling filter were activated in 10 days and 30 days respectively. 70%~85% of COD and 80% of TP were removed by TF when the hydraulic surface load was between 3~6.3 m3/ (m2·d). The removal effect of ammonia decreased as the hydraulic surface load increased. The removal of COD was not affected by the COD load, but the ammonia removal first increased and then decreased as the COD load increased. The hydraulic surface load did not influence the ammonia removal and the ammonia in effluent was below 15mg/L when the ammonia load was less than 0.04kgNH4+/ (m3·d). The first 0.6 meter of the trickling filter removed 89% of COD, 71% of TP, and nitrification took place in 0.6~2.4 meter of TF. The concen-tration polarization led to the main membrane fouling. Good effluent quality of the system could be reused as greening water. As the cheap coagulant used in this process, low energy consumption and fewer sludge production in TF, high degree of automation in ultrafiltration and the reclamation of effluent, the coagula-tion-trickling filter- ultrafiltration can be the preferred technology for the domestic sewage treatment.The effluents at all levels of the coagulation-trickling filter-ultrafiltration process were divided into five components by XAD resins: hydrophilic fraction (HPI), hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), and transphilic neutral (TPI-N). The results showed that DOM in domestic sewage was mainly composed of HPI and HPO-A, the major molecular weight dis-tribution in 1~3.5 kDa and the main fluorescent material was the protein-like II. There was more carboxylic matter in HPO-A, more hydroxyl matter in TPI-A, more aliphatic compounds in HPO-N, more amide material in TPI-N. The coagulation obviously removed HPI, HPO-N, and TPI-N; changed the molecular weight distri-bution of DOM into higher molecular weight area; partially removed protein-like matter in HPO-N, TPI-N, TPI-A by adsorption and the organic functional group was less affected by coagulation. The degradation of protein-like in HPI, protein-like, carboxylic and polysaccharides materials in HPO-A and TPI-A took place in TF; the aliphatic, amide materials in HPO-N and TPI-N were degraded but not obvious as observed. The average molecular weight of DOM components except HPO-A was reduced after TF. Ultrafiltration retained about 10% of DOM components, including some humic-like acid, fulvic-like acid material and carboxyl, hydroxyl material in HPO-A, TPI-A; could not effectively remove the protein-like material, amide ma-terial in HPO-N, TPI-N. The average molecular weight and average molecular number of DOM components were lower after ultrafiltration.